5,804 research outputs found
Warped Brane worlds in Critical Gravity
We investigate the brane models in arbitrary dimensional critical gravity
presented in [Phys. Rev. Lett. 106, 181302 (2011)]. For the model of the thin
branes with codimension one, the Gibbons-Hawking surface term and the junction
conditions are derived, with which the analytical solutions for the flat, AdS,
and dS branes are obtained at the critical point of the critical gravity. It is
found that all these branes are embedded in an AdS spacetime, but, in
general, the effective cosmological constant of the AdS
spacetime is not equal to the naked one in the critical gravity,
which can be positive, zero, and negative. Another interesting result is that
the brane tension can also be positive, zero, or negative, depending on the
symmetry of the thin brane and the values of the parameters of the theory,
which is very different from the case in general relativity. It is shown that
the mass hierarchy problem can be solved in the braneworld model in the
higher-derivative critical gravity. We also study the thick brane model and
find analytical and numerical solutions of the flat, AdS, and dS branes. It is
find that some branes will have inner structure when some parameters of the
theory are larger than their critical values, which may result in resonant KK
modes for some bulk matter fields. The flat branes with positive energy density
and AdS branes with negative energy density are embedded in an -dimensional
AdS spacetime, while the dS branes with positive energy density are embedded in
an -dimensional Minkowski one.Comment: 14 pages, 7 figures, updated version, accepted by EPJ
Locating High-Impedance Fault Section in Electric Power Systems Using Wavelet Transform, k
High-impedance faults (HIFs) caused by downed conductors in electric power systems are in general difficult to be detected using traditional protection relays due to small fault currents. The energized downed conductor can pose a safety risk to the public and cause a fire hazard. This paper presents a new method for locating the line (feeder) section of the HIF with the help of limited measurements in electric power systems. The discrete wavelet transform is used to extract the features of transients caused by HIFs. A modified k-means algorithm associated with genetic algorithms is then utilized to determine the placement of measurement facilities. The signal energies attained by wavelet coefficients serve as inputs to the support vector machine for locating the HIF line section. The simulation results obtained from an 18-busbar distribution system show the applicability of the proposed method
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